Answer to Case 694

The following excellent answer to this week's case is by our guest author, Jacob Rattin (@eternalstudying), medical student and future pathologist. Hopefully we will be able to recruit him to my residency program at Mayo Clinic!

Answer to Parasite Case of the Week694: BAL showing a ciliated respiratory epithelial cell exhibiting ciliary movement.

If you reach back into your memories from undergrad cell bio, motile cilia contain “9+2” axonemes made up of 9 doublet microtubules and a central pair of microtubule singlets. The peripherally located “9+2” doublets are associated with several accessory proteins, with dynein arms being most relevant to us in this case. The dynein arms provide ATP-dependent motor function, with hydrolysis of ATP resulting in sliding of the axoneme and ciliary movement, which is what you are seeing in the video. The respiratory epithelial cell does not have to be a part of the tissue to exhibit their back-and-forth motion. If ATP is available for hydrolysis, the dynein arms will provide ciliary movement!

As a reminder, ciliated epithelium can be found in the following regions:

• Upper respiratory tract

• Fallopian tube and parts of the endometrium 

• Ependymal cells that line the ventricles in the brain 

• Caput epididymis/efferent ducts

• Locations in which ciliary metaplasia has occurred

Some folks on Twitter, LinkedIn, and in the comments section of this blog were thinking Lophomonas blattarum, a multiflagellate protozoan that occupies the gut of the cockroach Blatta orientalis. While there are similarities between the two regarding their morphology, there is no good evidence at this point that L. blattarum is a human pathogen, nor that it is found in BAL. What is often misdiagnosed or misidentified as L. blattarum is actually a ciliated respiratory epithelium in various stages of degeneration. Furthermore, molecular studies have questionable validity due to the non-specific PCR primers that have been used. In the comments, Richard Bradbury went into fantastic detail stating, “I reviewed the PCR primers used in these papers. The forward and reverse PCR primers in a standard “all-sequences on Genbank” BLAST showed the first series of hits to flagellates of various forms (L. blattarum and a lot of different trichomonads), all at 100% identity for both primers. This does raise the possibility that the positives they identified were actually Trichomonas tenax, which is normal oropharyngeal flora, or another unidentified commensal trichomonad of the oral cavity.

So, what’s next? We suggest sequencing of L. blattarum taken from the gut of the cockroach B. orientalis to compare to the ciliated respiratory epithelium (or, the purported L. blattarum) taken from a BAL. This would bypass the morphologic ambiguity that surrounds this issue and give us a more definitive answer.